This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The objectives of this research are focused on the molecular mechanisms that govern variant antigen gene expression in Plasmodium. Antigenic variation is a fundamental adaptation to evade a host protective immune response and is one of the major factors contributing to the establishment of chronic blood infections. The classic P. knowlesi-rhesus monkey model is amenable to both in vitro and in vivo studies and unique stable clones of the P. knowlesi H strain expressing distinct SICA (Schizont Infected Cell Agglutination) variant antigen phenotypes after induced sequential switchings can be maintained after numerous in vivo passages (60 generations) in naive rhesus monkeys. These isogenic clonal lines provide a special tool for studies of the cellular and genetic mechanisms underlying clonal antigenic variation. This year, we performed several new in vivo switch experiments and characterized the new switched SICA phenotypes using LC-MS/MS, bioinformatic tools and molecular biological tests. Several approaches were also undertaken to generate specific antibodies to defined SICA proteins and use these reagents in experiments relating to trafficking of the SICA proteins and switch events. We also established new collaborations with the Sanger Center in the UK to perform NextGen and RNAseq experiments to refine the P. knowlesi genome database. This was much welcomed as a follow-up to a report we published on the redefined SICAvar prototype gene and protein, which emphasizes the need for further attention on the closure of the Pk genome data.